The experiments outlined in this proposal are aimed at identifying the function of a proto-oncogene called yes. This cellular gene is highly expressed in cerebellum, retina, kidney and liver. Molecular, biochemical and biological approaches are proposed to determine which cells in these organs and tissues express the yes gene, and to identify cellular functions governed by this gene and its products. Polyclonal antibodies against the viral-yes protein, which recognize cellular-yes (c-yes) proteins, and monoclonal antibodies that recognize avian and rodent yes proteins will be used as probes. Attempts will also be made to map neuronal cells that express c-yes proteins by analyzing mutant in mice in which mutations cause death of one or more classes of cerebellar cells. Efforts will be made to identify and characterize proteins that are phosphorylated on tyrosine specifically in the cells expressing the yes proteins, which are tyrosine protein kinases. As a part of this project we will also analyze the mechanism of activation of the c-yes protein by polyoma middle T antigen and we will study the influence of post-translational modifications of the c-yes protein on its kinase activity. These studies may elucidate the mechanisms involved in regulating the c-yes protein kinase activity in normal cells. Structure of the yes proto-oncogene and the mechanism of c-yes transduction into the Yamaguchi 73 viral genome will be studied by sequence analysis of molecular clones. In addition, characterization of cDNA clones will be carried out to investigate differential splicing of c-yes transcripts. Analysis of the c-yes cDNA expression in a cloned retrovirus vector should provide information on the transforming potential of this proto-oncogene. If the c-yes cDNA expressed in a retroviral context is not transforming, we will map spontaneous mutations that convert the c-yes gene into a transforming gene. Functional and structural analysis of cellular proto-oncogenes may have broad implications for our understanding of the molecular mechanisms of neoplastic transformation and could provide some clues of strategies for controlling them.